Method of producing phosphate ceramic pipe cladding

ABSTRACT

A pipe cladding composition which is a phosphate ceramic permeating a non-woven fibrous network. The overall thickness of the sheet is between about 5 and about 20 mils. The phosphate ceramic permeates the fibrous network and extends beyond the fibrous network only up to a maximum thickness of about 3 mils across each side of the sheet. The sheets are prepared using wet reaction mixtures which produce phosphate ceramics. These reaction mixtures are mixed and pressed into the non-woven fibrous network which forms a wet sheet that is then cured to provide the cladding material.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 07,395,618, filed Aug. 18,1989, now U.S. Pat. No. 5,312,657.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to pipe cladding sheet materials. Suchsheet compositions are used to wrap insulated pipes. Insulation aroundpipes is held securely in place by these pipe cladding sheetcompositions.

2. The prior Art

Presently, pipe cladding which is being used is made frompolyvinylchloride. Although polyvinylchloride pipe cladding is punctureresistant and flexible enough to be wrapped around the insulated pipes,the polyvinylchloride is combustible. Even worse, when thepolyvinylchloride does burn, it gives off toxic gas.

It would be useful and even advantageous to have a low cost, more fireresistant replacement for the polyvinylchloride pipe cladding.

To function as pipe cladding, however, certain other requirements shouldbe met. Naturally, the composition being used as pipe cladding shouldwrap the cylindrical volume without breaking or cracking. The materialshould be in a sheet form and should definitely be relatively easy tohandle and install without breaking, puncturing or flaking off the sheetmaterial. For the best versatility in a commercial product, the pipecladding should be capable of wrapping around a cylindrical volumehaving a diameter down to 1.5 inches.

Although sheets could be used as pipe wrapping (cladding) without curlmemory, pipe cladding should, in its normal position, have a circularcurl and have curl memory, so that when it is unrolled or straightenedout of its normally cylindrical position, it will reassume a curledposition when it is released. This is referred to as "curl memory". Curlmemory makes the cladding sheet go around the circular pipe verynaturally. This makes it easy to cover the pipe and install thecladding. Curl memory is thus an important requirement for a pipecladding composition.

It has been discovered that pipe cladding sheet compositions can beprepared using phosphate ceramic. The compositions provided by theinstant invention are thin, relatively light in weight, andnon-combustible. Due to the thinness of the instant sheet compositions,rolls of these materials can be easily stored and transported. A minimumamount of space is needed for their storage and installation.

Summary of the Invention

The pipe cladding of the present invention comprises a thin sheet whichnaturally rests in a curled position, and has curl memory. The sheet hasa thickness in the range of from about 5 to about 20 mils and comprisesa reinforcing non-woven fibrous network and phosphate ceramic whichcompletely permeates the network. The non-woven fiber is itself asheet-like network and at least some of the fibrous network is made ofpolymer fiber which is needed for the cladding sheet to have curlmemory. Suitably, the non-woven fibrous network is provided by a scrim,mat, or web.

The "curl memory" is the tendency of the pipe cladding to return to itscircular, curled position. Sheets without this memory are difficult toinstall.

The non-woven fibrous network provides the flexibility, reinforcement,and is also used to form the sheet itself. In fact, the fibrous networkis largely responsible for giving shape and dimension to the pipecladding sheet material.

Naturally, if the sheet gets too thin, it will lack the durability,strength, and puncture resistance needed for use or desired forinstallation, although extremely thin phosphate sheets can be madehaving outstanding flexibility. The non-woven fiber network inside of apipe cladding sheet should have a thickness of about 5 mils or greater.Networks of at least about 5 mils in thickness also will have more thanthe minimum fiber density needed for the cladding.

It has furthermore been found that the phosphate ceramic cannot beallowed by itself in thick layers or thick patches over the surface.While ceramic build-up covering each side of the fibrous network ispermitted to some extent, compositions with thicker ceramic build-up areunsuitable for pipe cladding because such materials crack and break tooeasily when they are handled, used, or bent. Thus, in accordance withthe present invention, the permitted thickness of the ceramic coveringthe fiber is limited to provide the pipe cladding.

It has been pointed out that the instant pipe cladding compositionsshould not crack or break when they are used. The terms "cracking" or"breaking" are not intended to refer to the fine hairline fractures thatwill develop in the phosphate ceramic as the cladding sheet is flexed.These terms refer to complete separations, permanent bends, or ceramicloss from the sheet. Pipe cladding can be flexed and curled in acircular manner around a pipe without having permanent breaks, creases,or folds occurring.

The terms "sheet" and "sheet material" are used herein; such terms referto compositions having the dimensions of breadth and length much largerthan the thickness; such compositions are essentially two-sided, eachside being called a "face".

DESCRIPTION OF THE DRAWING

The drawing shows a cross-section of the instant pipe cladding. At thesurface (1) phosphate ceramic extends beyond the center portion (2). Thecenter portion (2) contains the fibers making up the nonwoven fibrousnetwork and the phosphate ceramic. Two indefinite boundries (3) exist oneach side of the nonwoven fiber. This is the point which could bevisually recognzied in the pipe cladding as the outermost point to whichthe fibrous network extends throughout the sheet. Beyond this point, thephosphate ceramic can extend. The thickness of the phosphate ceramicmaterial (1) over and beyond the outermost level of the fibrous network(3) is limited to provide a sheet material which can be wrapped aroundpiping, flexed, and handled without cracking or breaking the claddingmaterial.

DETAILED DESCRIPTION

The instant pipe cladding has a non-woven fibrous network. Althoughconceivably, this network could be provided by laying or stringingcontinuous fiber into the wet, reacting phosphate ceramic mixture andpressing out a sheet, conveniently and preferably non-woven fibrousscrims, mats, or nets are used to provide either all or part of thisnetwork.

Fibrous materials which are woven are less suitable; the looser weavesparticularity tend to segment the ceramic; tight weaves are not desireddue to lack of permeability. Weakened sheet compositions and those thatare prone to crack, break, and flake off bits of the ceramic frequentlyresult.

More than one non-woven scrim can be used. Even if more than one scrimis used, however, the same dimensional limitations will apply. Thethickness of the fibrous network is limited to obtain a pipe claddinghaving the necessary flexibility without the tendency to crack, break,or develop permanent folds and creases. Thus, the non-woven fibrousnetwork inside of a pipe cladding composition preferably should not havea thickness greater than about 16 mils. This is true whether or not thefibrous network is derived from a single or two or more non-woven netsor scrims put together. If more than one scrim is used, they should notrest apart in separate layers. Instead, they should be placed or pressedtogether to form a single interior network inside the sheet. Inpreparing the cladding material, it is permissible to ply a thin layerof wet, reacting ceramic mixture between such multiple scrims, but theceramic must be pressed, worked, or kneaded into them. The ceramicshould substantially completely permeate the fiber network throughout,while the scrims are pushed together so that there is a single interiornetwork.

Although the ceramic-fiber mixture does not have to be absolutelyhomogeneous, it is nevertheless a homogeneous combination to the degreethat the cladding material will not have any internal layers of ceramic,and they do not have a "fibrous layer" as such. To the contrary, in thepipe cladding, the phosphate ceramic permeates substantially all of thefibrous network.

The phosphate ceramic which is suitable to form the instant pipecladding compositions may be produced by a reaction of aqueousphosphoric acid, calcium silicate, and a metal oxide selected from thegroup consisting of: magnesium oxide, aluminum oxide, zinc oxide, andcalcium oxide. A preferred phosphate ceramic can be referred to ascalcium magnesium aluminum phosphate; this preferred phosphate ceramicis made with aluminum oxide and magnesium oxide.

This phosphate ceramic material and processes for preparing it is knownand has been previously described in references such as U.S. Pat. Nos.4,375,516 and 4,569,878. The U.S. Pat. No. 4,375,516 reference describesboth foamed and non-foamed phosphate ceramic compositions. In theinstant case, however, to prepare the pipe cladding sheet compositions,the reactants are mixed to produce the non-foamed phosphate ceramic.

For preferred pipe cladding materials, the phosphate ceramic can beprepared using a phosphate ceramic made by: mixing an aqueous solutionof phosphoric acid and aluminum oxide, and thereafter mixing in thecalcium silicate (wollastonite) and a metal oxide selected from thegroup consisting of magnesium oxide, aluminum oxide, calcium oxide, andzinc oxide. Based on 100 parts of calcium silicate, the total of allportions of the metal oxides added can be from about 11 to about 65parts by weight, and the aqueous phosphoric acid solution, which is fromabout 35 to 75 by weight of phosphorous pentoxide, can be used in anamount of from about 80° to about 190 parts by weight.

After the ingredients for the phosphate ceramic are mixed, the phosphatematerial will be "wet" and in the state of reacting and curing toproduce a dry, rigid phosphate ceramic. While this reacting mixture is awet fluid or paste, it can be screeded, pressed, or rolled until themixture sets (becomes rigid). Before the ceramic sets during curing,this wet mixture and the fibrous network can be worked together (such asby pressure and/or kneading) to form the cladding sheet; and thenpreferably it is pressed, curled into a circular position beforesetting, and is then permitted to set and finish curing in the rolledposition. Since the fibrous network contains an effective amount ofpolymeric fiber to have curl memory, cladding sheets made by thisprocess will have curl memory without the need to heat the cladding (andthe fiber), and then cool it. Heating and cooling, however, can be doneto obtain a stronger, more completely elastic memory.

In preparing the cladding, it is preferred not to use highly densefibrous networks because it can be extremely difficult to work the wetceramic into the sheet to the degree required. The fibrous network usedshould have a porosity high enough to allow the reacting wet phosphatematerial to permeate the network. The minimum porosity that is effectiveto allow permeation of the wet phosphate reaction mixture is used tomake the cladding. This viscosity will vary depending on otherconditions such as the amount of pressure used, the type of processingequipment, amount of kneading performed, and the viscosity of the wetphosphate reaction material.

Non-woven fiber sheets (like scrims and mats) which have a porositylevel that will give a minimum reading of about 600 cubic feet perminute (cf m/ft2) measured at 0.5 inch (in.) of water pressure (overatmospheric pressure) in the Frazier air permeability test will beacceptably porous and permeable enough for the wet fluid phosphatecement reaction mixture to penetrate.

A more preferred porosity level, however, is about 800 cf m/ft² measuredby the Frazier air permeability test at 0.5 in. of water pressure. Atthe higher levels, it will be easier to drive the fluid reaction mixtureinto the fibrous network. If desired, less pressure, less kneadingand/or even a more viscous reaction mixture can be used at these higherlevels of permeability.

A preferred non-woven fibrous network has a total thickness in the rangeof from about 5 to about 16 mils. The phosphate ceramic permeates thisnetwork substantially completely and does not entend beyond the fibersurface (beyond its indefinite boundry (3)) more than about 3 mils.These dimensions are needed to insure that the pipe cladding sheet canwrap the smaller pipes without breaking.

Although some sheets, in fact, might be used to wrap cylindrical volumeshaving only the larger diameters, and thus be able to have a thickerfibrous network, such pipe cladding is not commercially preferred. Forreasons of practicality, pipe cladding is used which Willie able to wrapall pipe sizes to be wrapped regardless of whether it is large or small.This avoids the necessity of having to change from one cladding materialto another during the course of wrapping (even a single pipe line canvary in diameter). It also avoids the necessity of maintaining differentcategories of cladding in an inventory. Practically speaking, therefore,a pipe cladding material should be flexible enough to wrap a pipe havingthe smallest diameter. The smallest diameters should probably be on theorder of about 1.5 inches.

If more flexibility is desired, the fibrous network can be made thinner;more preferably, the fibrous network has a thickness less than about 14mils. If the sheets are too thin, the ceramic can even abrade off justfrom handling them. Damage such as tears and holes will occur tooeasily. Thus, although very thin sheets can be formed, it is notsuitable pipe cladding. Practically speaking, therefore, the fibrousnetwork should be at least about 5 mils. More preferred thicknesses forthe fibrous network are in the range of from about 7 to about 14 mils inthickness or from about 8 to about 12 mils.

The fibrous network will provide enough support for a limited amount ofceramic to extend beyond the fibrous level. Although hairline fracturesdo tend to form in the ceramic, these fractures can be tolerated, sincethey will not cause actual breaks, bends, or tears in the sheet, andsince they will not result in damage or serious loss of the ceramic fromthe sheet. Limiting the extension of the ceramic beyond the fiber levelis one factor that helps to avoid the tendency to break and crack,causing permanent bends or damage to the sheet. Moreover, when thicker,non-woven fibrous networks are used, the maximum thickness of theceramic material covering the fiber surface is preferably even thinnerto insure flexibility without such breaking. For non-woven fibrousnetworks having a thickness of from about 7 to about 16 mils, thethickness of the ceramic coverin the fiber will preferably be less thanabout 2.5 mils. In fact, more preferably, the thickness of the phosphateceramic that extends beyond the fiber level is limited to a maximum ofabout 2 mils. The ceramic on each face of the network can be 0 but willnot be more than about 3 mils, an acceptable thickness being from 0 toabout 3 mils.

When the mixture of calcium silicate, metal oxide, and phosphoric acidis wet, it is fluid and pliable. The viscosity should be sufficientlyhigh to stay in the fibrous network (so that it does not flow out), andit is sufficiently low to penetrate and permeate the fibrous networkwhen the cladding is made. It is a permissible alternative to use a moreviscous wet mixture and insure a complete penetration of the fibrousnetwork by increasing the pressure and/or kneading action when combiningthe wet mixture and fibrous network or even using a more porous fibrousnetwork. It, however, is preferred not to have a wet mixture with aviscosity of greater than about 20,000 cps. At extremely highviscosities, the needed penetration into the fibrous network might notbe as good and the pipe cladding quality will be detrimentally effected.Most preferably, therefore, the wet mixture of the aqueous phosphoricacid, calcium silicate, and metal oxide should be used at a viscosity inthe range of from about 2,000 to about 12,000 cps. It has been foundthat the wet phosphate mixtures having viscosities within this rangehave excellent handling properties for preparing the pipe claddingsheets. Naturally, the higher viscosities, up to about 20,000 and evendown to about 12,000 cps, would best be used with thinner or more porousnon-woven fibrous networks. Thus, more viscous wet mixtures will be mostsuccessfully used and are preferred for the thinner and/or more porous,non-woven fibrous networks.

It has also been found that the best pipe cladding compositions will beproduced on a continuous line. In these instances, the fibrous networkis preferably provided by at least one non-woven web, mat, or scrimwhich is continuously pressed with a layer of the wet mixture of aqueousphosphoric acid, metal oxide, and calcium silicate. Thereafter, mostpreferably, the wet sheet is kneaded. It is then pressed and allowed tocure. The pipe cladding produced from a continuous production line willgenerally be far superior to pipe cladding produced by batch preparationmethods.

In another preferred embodiment, the wet mixture is used at viscositiesmore preferably in the range of from about 3,000 to about 9,000 CPS andit is continuously spread onto a face of the fiber network. The mixtureis pressed into the fiber network, and preferably, the wet phosphateceramic is then worked further into the network by a series of rollers.When more than one scrim is used, the ceramic is preferably spreadbetween two of them on one face. The amount of ceramic spread onto thefiber preferably is slightly in excess of the amount needed inside thefiber network. The plied layer of the wet, fluid phosphate cementreaction mixture preferably will not be more than about 6 mils thickerthan the total thickness of the non-woven fiber network being used. Thewet fiber-ceramic sheet is preferably then sent through a press, tosmooth out the sheet surface. In addition to smoothing the surface ofthe sheet, the press (either heated or not heated) can also have raisedand lowered areas to put an embossed feature into the wet ceramic of thewet sheet. This will produce a surface-textured cladding sheet.Preferably, the press is heated to speed curing. The final gauge of thecladding sheet can also be set at this point using the press.Preferably, the press will have maximum pressure between its middlepoint and the end from which the sheet exits. If-desired, this could bedone with a weighted load. Thereafter, the sheet can be rolled dp to setand finish curing. After it is completely cured, it will be dry andready to use. The cladding is easily stored or transported in rolls. Ifdesired, carrier paper can be used.

After pressing the wet mixture into the fibrous network, if desired, thewet, fiber-ceramic sheet can be given enough heat to raise itstemperature to a point in the range of from about 53° to about 65° C. inorder to speed the curing.

At least two methods can be used to put curl memory into the pipecladding composition. One is by heating the sheet when it is in thedesired curled position. Another is to cure and set the ceramic whilethe sheet is rolled. Preferably, both are used. Heating can even be doneto the wet cladding composition of phosphate ceramic and fibrous networkas the wet reaction mixture cures to form the rigid, phosphate ceramic.

The amount of heat which is used must be effective to heat but notsoften the synthetic polymer fibers inside the sheet while it is curledor rolled up. After the polymer fibers have heated, but not melted, thesheet is cooled before allowing the sheet to be unrolled. This heatingstep can be done before, during, or after curing and setting of thecladding composition. It can even begin before setting of the phosphateceramic takes place, and finish during or after curing.

Since the cladding sheet has a curve, unless it is held down, it willnot rest in a flat position even if it is cut into short pieces. Shortpieces of the cladding sheet will have the form of an arc in thedirection of its curved surface. Longer pieces of the cladding sheetwill curl, to completely form a circle or circular roll. Thus, with thecurl and the curl memory, the pipe cladding sheet will rest in acylindrical position when the sheet has a sufficient length to form acircle.

Even if the curve is slight so that the diameter of the naturally formedcircle is large (up to two feet or even more), the sheet will still beflexible enough to wrap a 1.5 diameter pipe without cracking orbreaking. Preferably, however, the cladding sheet is given a curl thatwill allow the sheet to naturally form circular shapes with a diameterless than about 10 in. Most preferably, it will naturally curl into acircle with a diameter less than about 5 in. The cladding sheets thatcurl into the smaller, tighter circles readily and naturally are easierto install, and will fit better around the pipe.

For the sheet composition to have curl memory, an effective amount ofthe fibers in the network will be made of a polymer (includingcopolymers). This is true regardless of the method used to get the curland memory into the cladding sheet. The pliability of the polymer fibersis required. Preferably, at least about 65% by weight of the fiber inthe nonwoven fibrous network is made of polymer. More preferably,polymer fiber will be used for all of the non-woven fibrous network.

Preferably, the polymer has a glass transition temperature less thanabout 350° C. Although it is not necessary that the polymer actually beheated to the softening point. Heating below the softening point issufficient to set the curl memory. Preferably, the synthetic fiber willhave a glass transition temperature in excess of about 90° C.; the glasstransition temperature can be in the range of from about 90° to about350° C. Fibers which can be heated to set the curl memory can, forexample, be made of a member selected from the group consisting of:polyvinyl chloride, polyamid, polypropylene, polyester, polyethylene,polyolefin, polyvinyl-alcohol, acrylic polymers and copolymers, acetatepolymers and copolymers, and fluorocarbon polymers and copolymers. Morepreferably, the fibers will be made of a material selected from thegroup consisting of: polyester and polypropylene.

Although it is permissible to have a small amount of fiberglass in thenon-woven fibrous network, this is not preferred. Fiberglass tends to bemore brittle and is too rigid. Sheets made with non-woven fiberglassnetworks, moreover, cannot be given the needed curl memory even if theceramic sets and cures while the sheet is in a rolled position. Suchsheets also will lack the needed pliability for pipe cladding.

Fortunately, the phosphate ceramic itself is a very non-flammablecomposition and with this ceramic permeating the fiber, even moreflammable fibers can be used. Surprisingly, in fact, even thoughflammable fibers are used, the pipe cladding sheets are surprisinglyfire resistant due to the complete permeation of the phosphate ceramicthroughout and over the fibrous network.

When the pipe cladding is needed, it can be unraveled and coiled aroundthe insulated pipe. The loose seams of the pipe cladding can be securedby such means as an adhesive, rivits, staples, or by ties which areplaced around the cladding.

If desired, a coating composition can be put over the top of thephosphate ceramic to improve handle-ability and improve the feel of thepipe cladding sheet when it is touched. This could also be desired as avapor barrier. Any coating material such as resins or latexes could beused. For example, an acrylic latex or resin could be used. Thethickness of the coating is not critical; such coatings are normallythin, having the approximate thickness of a paint coating. The coatingwill not require a change in the dimensions of the cladding sheet. Thecladding could even be painted. If desired, dyes or pigments could bemixed into the phosphate ceramic mixture to give the cladding color.

The Examples which follow are offered to illustrate the instantinvention and should not be taken to limit it. All parts and percentagesare by weight unless otherwise indicated.

EXAMPLES Preparation of the Wet Ceramic Mixture

The wet phosphate ceramic mixtures for the following examples were madeaccording to the following formula:

    ______________________________________                                        Ingredient       Parts By Weight (Wt.)                                        ______________________________________                                        Al.sub.2 O.sub.3.3H.sub.2 O                                                                    7.2                                                          MgO              4                                                            CaSiO.sub.3      58                                                           75% H.sub.3 PO.sub.4 (53.0% P.sub.2 O.sub.5)                                                   54.2                                                         H.sub.2 O        8.6                                                          ______________________________________                                    

The wet ceramic mixture was prepared by mixing the phosphoric acid, thealuminum oxide, and the water until a clear solution was obtained. Thenthe solution was cooled to 4° C. and a mixture of the MgO andwollastonite (calcium silicate) was added with vigorous mixing in an airstirrer. The phosphate ceramic prepared using this formula can bereferred to as a calcium aluminum magnesium phosphate. Although thispreparation is most preferred, other preferred ceramics can also beprepared using different concentration ratios, sequences of additionand/or even other metal oxides.

Example 1

A drawdown of the previously described wet ceramic mixture was made ontoa polyester scrim (2011 from DuPont) that was 12×12 in. The scrim was 1oz/sq. yd. and was 7 mils thick. The drawdown was made at a thickness of12 mils over the face of the fiber. To force the wet ceramic mixtureinto the fibrous network, it was then pressed for two minutes at 75 psi,simultaneously it was heated at 180° F. to speed the reaction. It wasthen removed. When the ceramic finished curing, the sheet could bewrapped around a 1.5 inch diameter pipe without cracking and withoutpermanent breaks.

To give the composition curl memory, the sheet would be rolled and putinto an oven at a temperature in the range of from about 125° to about230° C. for about 0.5 to about 4 minutes to heat the polyester (itshould not actually soften). It would then be removed and cooled.

The dried, cured sheet of this example was 11 mils thick. Theceramic-fiber mixture inside was, of course, 7 mils thick, and theceramic covered the fiber on each side in a thin coat which was probably2-2.5 1.85-2.2 mils thick (averaging 2 mils in thickness) over eachface.

Example 2

The previously described wet mixture was used according to the procedureset forth in Example 1 to make a pipe cladding sheet. A non-wovenpolypropylene scrim 1.4 oz/sq. yd. and 8 mils thick (from DuPont) wasused as the non-woven fibrous network. The finished sheet could wrap a1.5 inch diameter pipe without breaking or cracking, and was 11 milsthick.

Example 3

This example demonstrates the preparation of pipe cladding that used twoplies of a 4 mil thick polyester scrim to provide the non-woven fibrousnetwork.

The non-woven polyester scrim (2250 polyester from DuPont) which was 1oz/sq. yd. was coated with a 12 mil drawdown of the formula previouslydescribed. A second ply of the same type of polyester scrim was placedon top of the drawdown and the sample was immediately pressed at 180° F.and 75 psi for two minutes. This drove the wet ceramic into the scrimsand forced the scrims together. When the sample was removed, it had athickness of 12 mils. It contained a non-woven fibrous network ofapproximately 8 mils thick. It was noted that the sheet had a thinceramic coating on each side which covered the fiber. It is estimatedthat the coating on each side ranged between about 1.9 and about 2.1mils thick. It had a tensile strength of 650 psi, and could be wrappedaround a 1.5" diameter pipe without cracking.

Example 4

The pipe cladding sheet material was prepared on a continuous productionline. A single ply of 7 mil thick polyester scrim (2011 -DuPont) wasused to provide the non-woven fibrous network. The previously describedwet phosphate ceramic mixture was drawn down onto a face of the scrim ata thickness of 9 mils. The ingredients for the wet phosphate mixturewere continuously mixed on a Respecta mixer and continuously plied ontothe scrim using a roll coater. The coated scrim was pulled through aseries of rollers which served to knead and work the wet mixture forcingit into the network. From there, the sheet was pulled (at an 11 secondresidence time), into a flat, heated press which ironed the materialsmoothing the ceramic on each side of the scrim, and which finished thesheet to a final gauge. The press was maintained at an overalltemperature of 155° F., and had a 500 lb. load centered 4.5 cm from theend out of which the sheet exited. Thereafter, the sheet was pulled intoand through a set of laminating rollers and from there was rolled onto aroller. The ceramic in the sheet had not set and was still curing. Afterapproximately two minutes, the ceramic had set.

When strips of the sheet were cut from the roll and were flattened out,the sheet material would return to its circular, curled position. Thus,the pipe cladding was given memory by maintaining the sheet in acircular roll as the phosphate ceramic mixture cured and set.

Although the cladding sheet did have memory, if desired, the rolled pipecladding sheet could be heated as indicated previously. After from about1/2 to 4 minutes, the cladding would be removed from the heat, and thememory would be even stronger.

Example 5

Using the procedure generally described under Example 4, a pipe claddingsheet was prepared using two plies of a 4 mil thick polyester scrim(2250-DuPont). The same continuous line apparatus was used as was usedfor Example 4. In this example, however, the previously described, wetphosphate mixture was drawn down on the face of one scrim at a thicknessof 11 mils. The second scrim was continuously plied onto the wetmixture. The scrims were forced together and the wet ceramic mixture wasworked through each scrim and out over the outer face of each scrim bypassing the scrim-ceramic mixture sheet composition through the seriesof rollers. The wet sheet then passed through (at 11 seconds residencetime) a press heated to 150° F. to iron the ceramic mixture which coatedeach outer surface, set the gauge of the final sheet thickness, andspeed curing. A 500 lb. load was used while pressing. The sheetthereafter went through the laminator and thereafter was rolled up ontoa roller. Since the wet ceramic was still curing, the cladding sheetwould, after curing, have curl memory. In this case, however, thecladding sheet material was placed into an oven set at a temperature of134° C. for a time of 3 minutes. After this time, the Poll of pipecladding was removed. The cladding sheet had an overall thicknessranging between 12 and 13 mils, a natural curl that allowed it to restin a cylindrical position, and curl memory.

The pipe cladding prepared under this example was also tested for itsability to wrap piping. It was found that the sheet material could wraparound a 1.5 inch diameter pipe without breaking.

Cure Memory Test

When a meter long strip (about 4-6 inches wide) of the finished pipecladding sheet was cut from the roll, the curl memory was tested bysecuring one end, and allowing the curled sheet to drop in a verticaldirection (by gravity). The curl memory was so strong that the sheetrolled back up into its circular position. Pipe cladding sheet materialswhich were given curl memory by rolling the sheet while the ceramicmixture cured were also given this test for the curl memory. It wasnoted that such sheets also rolled up and returned to the circular,curled position.

Example 6

This is a comparison example which is offered to show that glass fibercannot be used as the non-woven fibrous network for pipe claddingmaterials. Even though the sheet might be curled as the phosphateceramic cures, such sheets will not return to the circular, curledposition using the test method described under Example 5.

A single ply of a fiberglass mat which weighed 4 oz per linearmeasurement (from Superior Glass Company) was coated with a 12 mil drawdown of the previously described wet ceramic mixture. The sample waspressed at 75 psi and heated to 180° F. for two minutes forcing the wetceramic through the fiberglass and out onto the other side. The sheetwas then rolled up into a circular position while the phosphate ceramiccured, set, and dried.

The finished sheet had a thickness of 12 mils and could wrap a 3 inchdiameter pipe without cracking.

A strip of the sheet was given a test for its curl memory by holding itin its rolled position, and releasing the sheet while one end wassecured. The sheet unraveled, falling downward. The end of the sheet,however, did not recoil and thus, was unable to retain its curl memory.

A portion of this sheet was cut away from the roll and was examined forflexibility. The sheet was not as flexible as the other materials madewith polyester or polypropylene fibrous networks. It was also noted thatglass fibers were exposed at the cut edges which gave the material poorhandling properties.

What is claimed is:
 1. A method for preparing a phosphate ceramic pipecladding sheet having curl memory, comprising, pressing together (i) atwo-faced, non-woven fibrous network which contains polymeric fiber, thenetwork having a minimum thickness of about 5 mils and (ii) a wetmixture of calcium silicate, an aqueous phosphoric acid solution, and ametal oxide selected from the group consisting of aluminum oxide,magnesium oxide, calcium oxide, and zinc oxide, so that the wet mixturepermeates the fibrous network and a wet sheet is formed; placing the wetsheet in a cylindrical, rolled position; and curing the wet mixture toform the phosphate ceramic pipe cladding which has a total thickness ina range of from about 5 to about 20 mils, further providing thatphosphate ceramic covers each face of the fibrous network in a thicknessof up to about 3 mils.
 2. A method as described in claim 1 wherein thepolymeric fiber includes heat softenable fibers and wherein, the wetsheet is heated in the cylindrical position as it cures so that the heatsoftenable fibers are heated but not softened.
 3. A method as describedin claim 1 wherein the wet sheet is heated while it is in thecylindrical, rolled position.
 4. A method as described in claim 1wherein a series of rollers are used to press together the non-wovenfibrous network and the wet mixture.
 5. A method as described in claim 1wherein the wet sheet is pulled through a press before curing to givethe wet mixture a smooth surface and give the sheet a final gaugedthickness.
 6. A method as described in claim 5 wherein the press isheated.
 7. A method as described in claim 5 wherein the press also putsan embossed feature into the wet sheet.
 8. A method as described inclaim 1 wherein a continuous production line is used to form the wetsheet.
 9. A method for preparing a phosphate ceramic pipe claddinghaving curl memory comprising 1) pressing together (i) a two-faced,non-woven fibrous network which contains polymeric fibers which are heatsoftenable, the network having a minimum thickness of about 5 mils and(ii) a wet mixture of calcium silicate, an aqueous phosphoric acidsolution, and a metal oxide selected from the group consisting ofaluminum oxide, magnesium oxide, calcium oxide, and zinc oxide, so thatthe wet mixture permeates the fibrous network and a wet sheet is formed;2) curing the wet mixture to form a phosphate ceramic sheet compositionhaving phosphate ceramic on each face of the fibrous network at athickness of up to about 3 mils wherein the phosphate ceramic sheet hasa total thickness in a range of from about 5 to about 20 mils; and 3)placing the phosphate ceramic sheet in a cylindrical, rolled positionand heating the phosphate ceramic sheet to obtain the phosphate ceramicpipe cladding, further providing that the heat softenable polymericfibers are heated but not softened.
 10. A method as described in claim 9wherein a series of rollers are used to press together the non-wovenfibrous network and the wet mixture.
 11. A method as described in claim9 wherein the wet sheet is pulled through a press before curing to givethe wet mixture a smooth surface and give the wet sheet a final gaugedthickness.
 12. A method as described in claim 11 wherein the press isheated.
 13. A method as described in claim 11 wherein the press alsoputs an embossed feature into the wet sheet.
 14. A method as describedin claim 9 wherein a continuous production line is used to form the wetsheet.